1. Field of the Invention
This invention relates to propagation techniques for moving magnetic bubble domains in a magnetic medium, and to improved techniques which do not require shaped propagation structure such as magnetic elements along which poles are created for domain movement or conductor patterns, or which may be used to enhance or change the operation of conventional propagation structures.
2. Description of the Prior Art
Magnetic bubble domains have been moved in various magnetic media using a wide variety of techniques. For instance, bubble domains have been moved by using repetitive patterns of current conductors and by repetitive patterns of magnetic elements, such as the familiar T-I bars, chevrons, zig-zag bars, and disk shaped structures. The magnetic elements comprising conventional propagation structures can be comprised of magnetic material, such as permalloy, or can be comprised of ion implanted regions in the magnetic medium in which the domains exist. Generally, these magnetic propagation structures rely on the interaction between the propagation elements and a magnetic field in the plane of the magnetic medium, in order to establish a sequence of attractive magnetic poles for movement of the bubble domains. On the other hand, the current carrying conductors provide gradients in magnetic field normal to the plane of the magnetic medium in which the bubble domains exist, for movement of the domains in the medium.
The present invention differs from the propagation techniques used in the prior art, in that bubble domains can be moved in a desired direction in a magnetic medium without requiring shaped propagation structure such as discrete magnetic elements, and without requiring conductor circuits. It has been discovered that magnetic bubble domains in a magnetic medium distort in the presence of an in-plane magnetic field, and elongate in a direction along or opposite to the direction of application of the magnetic field depending on the polarity of the domains. In order to move the bubble domains in a preferred direction, an asymmetry is created in the in-plane magnetic field. For instance, the amplitude versus time or the shape versus time of the applied in-plane magnetic field can be varied in order to provide the asymmetry needed for motion in a particular direction. Further, the asymmetry can be provided by magnetic elements as will be described later. Thus, improvements can be made in existing propagation structures and new propagation structures can be provided for movement of magnetic bubble domains with a minimum of complexity of the propagation pattern.
Accordingly, it is an object of the present invention to provide essentially structureless shift registers for movement of magnetic bubble domains.
It is another object of the present invention to provide magnetic propagation structures for moving magnetic bubble domains, which do not rely upon on the creation of magnetic poles along the magnetic structure in order to move the domains.
It is a further object of the present invention to modify conventional propagation structures to provide improved operation with those structures.
It is another object of the present invention to move magnetic bubble domains in a magnetic medium in a way which minimizes the structure required for such movement.